The present invention relates to a defect information processing apparatus and method for capturing an image on the cylindrical surface of, e.g., a photosensitive drum or the like, and detecting defect information that pertains to smoothness or uniformity from the captured image data.
In recent years, the resolutions of images formed by copying machines and the like and those displayed on liquid crystal displays and the like have become higher beyond that of the human eye. Along with the advance of such technique, small defects present on the surface of a photosensitive drum, developing sleeve, liquid crystal display board, or dedicated printing paper used in the copying machines, printers, or the like have serious influences on higher resolutions. Also, a defect itself to be detected becomes very smaller as the resolution becomes higher.
FIG. 7 is a circuit block diagram of a conventional defect information processing apparatus.
As shown in FIG. 7, a conventional defect information processing apparatus scans the surface to be inspected of an object under inspection with a laser beam, and inputs an analog image of the surface to be inspected by a light receiver. From the analog image, unnecessary frequency components are removed by an analog filter 91, and that image is converted from an analog signal into a digital signal via an A/D converter 92. The image data is stored as multi-valued image data in an image memory 95. Also, the image data is converted into a binary signal via a binary converter 93 and the binary signal is stored in a binary image memory 96.
A CPU 94 computes defect data corresponding to a certain defect on the surface to be inspected on the basis of the multi-valued image data stored in the image memory 95, and the binary signal stored in the binary image memory 96, and stores, as feature data, the maximum and minimum values, the number of pixels, the coordinates, and the like of the defect data in a feature data memory 97. The CPU 94 checks based on the feature data stored in the feature data memory 97 if the object to be inspected is defective, and displays the checking result on a CRT or the like via an output interface 98.
However, since the filter used in the conventional apparatus is effective only for an image in the main scan direction of the laser beam due to its time-serial operation, if no change is found in the detection signal in the main scan direction, defect data cannot be obtained via the analog filter. For example, when an aluminum photosensitive drum is prepared by drawing, and a defect such as a thin scratch is formed in the longitudinal direction of the cylindrical surface of the drum, since nearly no change is detected in the detection signal even by scanning in the longitudinal direction (main scan direction) of the drum, the defect can hardly be detected.
In order to solve this problem, when a two-dimensional spatial filter is used, and the filter size for the sib-scan direction of a laser beam is set to be 5 lines or more, the hardware scale and cost increase, and DSP software processes are slow.
The present invention has been made in consideration of the aforementioned problems and has as its first object to provide a defect information processing apparatus and method which can form a large-size filter by a simple circuit, and can achieve a cost reduction and high-speed processes.
It is the second object of the present invention to provide a defect information processing apparatus and method which can further increase the filter size, and can improve the defect detection performance.
It is the third object of the present invention to provide a defect information processing apparatus and method which can form an arithmetic device by a simple circuit, and can achieve high-speed processes.
In order to solve the aforementioned problems and to achieve the above objects, a defect information processing apparatus of the present invention comprises the following means. That is, there is provided a defect information processing apparatus comprising:
image input means for capturing a two-dimensional image of an object to be inspected;
digital conversion means for converting the two-dimensional image into multi-valued digital image data;
vertical filter means for filtering the multi-valued digital image data in a vertical direction;
horizontal filter means for filtering the multi-valued digital image data, which has been filtered by the vertical filter means, in a horizontal direction;
binarization means for converting the multi-valued digital image data, which has been filtered by the horizontal filter means, into binary data on the basis of a predetermined reference value; and
detection means for detecting a defect portion of the object to be inspected on the basis of the multi-valued digital image data and binary data,
wherein the vertical filter means comprises vertical difference computation means for computing a difference value of the multi-valued digital image data within a predetermined range in the vertical direction, and vertical weighting means for weighting the difference value computed by the vertical difference computation means, and
the horizontal filter means comprises horizontal difference computation means for computing a difference value of the multi-valued digital image data within a predetermined range in the horizontal direction, and horizontal weighting means for weighting the difference value computed by the horizontal difference computation means.
A defect information processing method of the present invention comprises the following steps. That is, there is provided a defect information processing method comprising:
the image input step of capturing a two-dimensional image of an object to be inspected;
the digital conversion step of converting the two-dimensional image into multi-valued digital image data;
the vertical filter step of filtering the multi-valued digital image data in a vertical direction;
the horizontal filter step of filtering the multi-valued digital image data, which has been filtered in the vertical filter step, in a horizontal direction;
the binarization step of converting the multi-valued digital image data, which has been filtered in the horizontal filter step, into binary data on the basis of a predetermined reference value; and
the detection step of detecting a defect portion of the object to be inspected on the basis of the multi-valued digital image data and binary data,
wherein the vertical filter step comprises the vertical difference computation step of computing a difference value of the multi-valued digital image data within a predetermined range in the vertical direction, and the vertical weighting step of weighting the difference value computed in the vertical difference computation step, and
the horizontal filter step comprises the horizontal difference computation step of computing a difference value of the multi-valued digital image data within a predetermined range in the horizontal direction, and the horizontal weighting step of weighting the difference value computed in the horizontal difference computation step.
As described above, according to the present invention, even for a defect that changes slightly in the main scan direction, a large detection signal can be obtained by providing digital filters having large numbers of taps in the horizontal and vertical directions.
By satisfying the required filter function while suppressing the circuit scale of the filter process in the main scan direction, the defect detection performance can be improved, and the apparatus cost can be reduced.
Since the number of stages of the filter process is not limited, the performance for emphasizing a defect signal improves.
Therefore, the quality guarantee precision of products inspected using the apparatus and method of the present invention can be improved, and the manufacturing cost can be reduced.